Optimization Of Heat Exchanging Network Of Straw Into Oil Based On Exergy Analysis

With the growth of energy demands, biomass has great potential as a renewable and clean feeds for producing modern energy carriers. According to our national conditions, developing biomass liquid fuels is inevitable.Biomass into oil (BTO) processes consist of biomass collection, biomass fast pyrolysis, bio-oil gasification, water gas shift, acid gas removal and CO2 capture, Fischer-Tropsch (FT) synthesis, syncrude refining and tail gas treating. In this paper, taking straw as biomass stockfeed and setting up the Aspen Plus simulation of BTO processes. Based on the simulation results, this paper integrates the pinch and exergy analysis in the heat exchanger network (HEN) of biomass into oil processes. The exergy analysis was applied to calculate the exergy distribution of straw fast pyrolysis and FT synthesis reaction unit, which indicated the maximum exergy losses equipment. Via process optimization reduce the exergy losses of BTO processes. Involved the main content includes:First, the initial HEN of the biomass into oil processes was analysed by exergy analysis. For the full recovery of the streams'heat, serveral streams were added to the original HEN. With Aspen Energy Analyzer software as the calculating plant, the pinch analysis as theoretical basis, the relation was analyzed between Minimum approach temperature and yearly cost. The HEN was rebuilt to recovery heat at an appropriate pinch temperature. In order to obtain the maximum heat recovery, which use the pinch analysist to restablish the new heat exchanger network. And the exergy analysis was used to analyse all the heat exchangers in HEN, which identified the exergy efficiency of each heat exchanger and find the low exergy efficiency links. The results show that the total annual cost of BTO processes could be reduced lowest by optimizing minimum temperature difference to 5 ?. In addition, the new and the original HEN were compared in economic aspects, the results showed that the former can get desired benefits by caculation, with less investment and large return.Secondly, based on the Aspen Plus simulation results, the exergy analysis was applied to calculate the exergy distribution of straw into oil processes. The results demonstrate that the two-stage gasifier, reverse-flow autothermal reforming reactor and FT reactor contribute 54.66% of total exergy losses and are the top three exergy losses equipments, with exergy efficiency 71.21%?56.43% and 57.57%, respectively. Among these three equipments, FT reactor is the lowest exergy efficiency and most exergy consuming one. The exergy efficiency of the processes was increased to 86.20% and exergy loss was reduced by 38827.6kW, via increasing the temperature of pyrolysis reactor, two-stage gasifier and FT synthesis reactor, reducing oxygen equivalent ratio in two-stage gasifier and improving oxygen equivalent ratio in reverse-flow auto-thermal reforming reactor.